[FIX] hr_work_entry_holidays: prevent not being able to cancel time off

Prior to this commit if work entries/payroll was installed you could not
cancel a time off in the future if the work entries were generated for
that period, however you should still be able to cancel a time off as
long as the work entries have not been validated yet.

TaskId-2791386

closes odoo/odoo#94165

X-original-commit: 975ac8d2a1809bf7725d577b0fa9143a5b255e0d
Related: odoo/enterprise#28673
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>